Object moving thru a fluid medium

(Thread Title : Object moving thru a fluid medium)
Yes, you seem to be right. Although as water is a fluid, I thought that reasoning might be equivalent.

 

Correct: P=F/A
Water is not compressible, so the resistances curves are quite different than those for a gas. Also, there is no cavitation with a gas.

 

I do not know what resistance curves you're talking about. But it does not matter.
I believe that the formula that gives the viscous resistance to an object totally submerged in a fluid is the same whatever the fluid. It must be taken into account, of course, that the density of fluids is different.
Neither would be cavitation in the water, if we could remove the dissolved oxygen in it. Cavitation only occurs when there are two different fluids in play. One of them must be a gas.

 

Thank you for making an attempt to answer my question. So far, you are the only one that has. That said, I love watching you guys argue.

Yes, a larger cross section would increase drag. That I already know. Its pretty intuitive. But in my simplified example, if I had two rows and two column of squares with sides of one unit each then I would have four squares totaling 16 units of "surface". If I combine those squares into one large square I only have 8 total surface units. In other words, if the train is larger in cross section then it has less surface than a longer train with the same amount of volume. Am I incorrect about this and if so, why?

 

Well, it is supposedly about objects moving through fluids. It does lack the punch of the notorious "submarine train" thread which graced this site, stimulating lively discussion, not to mention gales of laughter !

 

That reminds me of the scene in Fast and Furious Whatever with the 120mph sub crashing thru ice while chasing a sports car. What people don't realize is that the sub is actually evaporating the water directly in front of the sub with a MacGuffin Device and then channeling that evaporated water into a ramjet. This reduces the surface drag on the sub tremendously and the only thing the upgraded nuclear reactor has to overcome is the resistance posed by the ice and the ice will actually break up pretty easily at 120mph assuming that you've built your sail and foreplanes to accomplish such a task, anyways, and something like that requires quite a bit of forethought as to what you will be using your sub for.

My train does go under ice and water though, now that I think about it. I'm not really too sure you could build a 51 mile bridge over that deep a gully. Plus if you build a bridge you have to consider ice flows. I thought it might be fun to break them up with howitzers before they got to the bridge pylons. But then what do you do if you there's a polar bear on the ice flow? Do you still use the howitzer? No, you couldn't because then all the libbies would be up in arms and aghast at your brutality. And so you have to pay a helicopter crew to go out to get the polar bear. And there are labor costs to consider. Do you really want to have to pay a full time helicopter crew to go out the ice flows every few days? No, you don't. And so you build a tunnel instead.

 

Here, lemme sum it up for you in a few simple words from a poem I wrote. I find simple words often times convey meaning best because they can often mean more than one thing. Its just that their meaning is a little more spread out.

A pie, up high in the sky, this guy,
A pie up high in the sky.
Made fly a pie up high in the sky
made fly a pie up high
Why fly a pie up high in the sky?
Why fly a pie up high?
To fly up high in the sky this guy,
to fly up high in the sky.
"Why else would you fly a pie up high?"
said I, with a wry sigh
Because the day comes nigh
when as much as I try
I still must say goodbye.
All men die but only some men fly
out of the graves where they lie
attached to the pie that they flew to the sky
when they were still just this guy.

That's my favorite poem and I wrote it and if nothing else, at least I've got that.

Now then. I have given you entertainment. Please don't say that I haven't. In return, I would like for somebody to please answer my original question so that I can move onto other things.

Thank you and best wishes,

Patrick Hickey

 

Not enough treats do I bring? What about riddles, you guys like riddles? Here's a riddle I wrote. See if you can figure out what the answer is, because nobody else seems to be able to.
http://brainden.com/forum/topic/17909-submitted-for-your-perusal/
Yes, that was a bit pretentious and thank you for noticing! But it is also entirely genre-less, so there's that. Because there's not really very many people that can build something that hasn't already already been proto-typed in some manner, especially if what is being proto-typed is the paradigm itself.

Thank you and best wishes,

The answer to one of the riddles, but thankfully.....not all of them.

 

It is a very complicated matter, if you overlook any of the many complications, the bigger cross section train might get permanently wedged in a tunnel. That would give you a subterranean train, a variation on the submarine version.

 

If it got wedged in the tunnel, we would probably have to fire our tunnel design crew but I imagine they would be smart enough to include a little leeway. Otherwise, its our fault for hiring stupid people. That reminds me of a story I heard once about NASA. When the Mars Orbiter Crashed because of a unit mismatch the head of NASA was asked by a reporter whether or not they would fire the personnel responsible for the mishap. His answer was "when you fire the smartest guys in the world, who do you replace them with?"

There are already subterranean trains. This one would only be subterranean when it needed to be. The tunnel size on that would be astronomical and its probably best for there to be as few of them as possible. That said, because of the increased length and width of the cab, the train would have to run on a straighter track and a straighter track thru mountains necessitates increased tunnel usage. Although bogey science has come a long way since we invented Common Gauge Rail, so I guess we'll see.

 

Bogie or bogey ?

 

"Actually, you just have to zealot", he chuckled.

 

Depends if its a double or a triple.

 

Although I am a firm believer in bogey science. Heck, anybody can hit par. Thats why its called "par".

 

It depends.

Yes, but only from the standpoint of skin friction drag.

Yes.

What you're missing is the drag is due to several sources, not just skin friction. Four bodies could have less total drag or more total drag than a single body of the same total cross sectional area, depending on how they are shaped. The pressure drag of the four bodies could be enough less to make up for the increased wetted surface area.

Really - read through Hoerner's Fluid Dynamic Drag. It's quite accessible and doesn't require any more than a High School understanding of mathematics. If you genuinely want an answer, then you should do at least this much homework.